In Li-sulfur batteries, the diffusion of polysulfide ions, the poor electrical conductivity of elemental sulfur and insoluble Li2S or Li2S2 cause significant capacity fading, low coulombic efficiency and insufficient cycle life. One strategy to solve the above issues is to confine elemental sulfur in a porous and conductive carbon matrix, which can not only function as conductive pathway, but also provide efficient physical confinement or chemical bonding to trap the soluble polysulfides. Sulfur loading in the micropores, where the character of the sulfur is chain-like, results in inhibiting the dissolution of polysulfide ions and good cycling performance. Various carbon hosts were designed, such as carbon molecular sieve, carbon nanotube, microporous graphene. However, there are still needs for carbon hosts which are easy to be manufactured.
Main challenges for sulfur-carbon composite electrode, are how to increase the content of sulfur loading in the carbon matrix to achieve higher capacity, and to tune the size and shape of pores as well as the pore-size distribution and specific surface area for more efficient polysulfide confinement. Moreover, the low electronic conductivity of carbon matrix is a hinder for fast lithium ion diffusion, high sulfur utilization for achieving high columbic efficiency and good rate capability. Besides, preparation process for most micro-porous carbon substrates was time-consuming and difficult for reproducibility.